Curing of polyisobutylene



United States ,Pate'r'it o CURING F POLYISOBUTYLENE "ice . by the process of the invention as applied to polyisobutylene stocks loaded with carbon black. In general, it

has been found that treatment of carbon-black-containing polyisobutylene-stocks with sulfur and t-butyl peroxide 5 by the process of my invention causes the tensile strength J li R, Littl P k k L k N, 1,, i t United of the stocks to be raised from less than 500 to more States Rubber Company, New York, N. Y., a corpothan 1400 pounds per square inch and their modulus ration of New Jersey (500% elongation) to be increased from about 50 to 100 or more. No g fi g g gaggi 1952 10 The behavior of the t-butyl peroxide in polyisobutylene and carbon black stocks containing sulfur has been found 1 Claim. to be unique. A large number of similar chemicals, e. g.,

t-amyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxyphthalate, alpha, alpha-dimethylbenzyl hydroperoxide,

This invention relates to the curing of polyisobutylene. etc., have been substituted for the t-butyl peroxide and Polyisobutylene is a completely saturated hydrocarbon no evidence of cure observed. elastomer. It is a high molecular weight solid resembling Similarly, sulfur-containing chemicals have been subunmilled crepe rubber in consistency at room temperastituted for the sulfur in the process of the invention. tures. It is probably the most stable of the commercially For example, a wide variety of Thiokols (alkylene polyavailable elastomers toward deterioration reactions. As sulfide plastics), and tetramethylthiuram disulfide (a wella consequence of this stability, it has not heretofore been known rubber vulcanizing agent), have been substituted possible to vulcanize polyisobutylene by any practical for the sulfur. These chemicals did not operate with the method. t-butyl peroxide to cause the polyisobutylene to cure.

It has now unexpectedly been found that polyisobutyl- Any amount of sulfur equal to at least one part per ene may be cured by heating it in the presence of sul- 100 parts of polyisobutylene may be used in my process fur and tertiary-butyl peroxide. The curing of the elasto obtain a satisfactory cure. Moreover, the degree of tomer is evidenced by an increased modulus and higher cure, as measured by the increased modulus at 500% tensile strength. elongation is substantially independent of the sulfur con- The following examples illustrate the process of the centration above about one part of sulfur. This is supinvention in more detail. Parts referred to are on a ported by the data presented in Table II. The stocks weight basis. described in Table II were prepared as was stock D in EXAMPLE 1 Example 1, except that the amounts of sulfur and t-butyl peroxide were varied. The stocks were press-cured for This example shows the vulcanization of a polyisotwo hours at 166 C. butylene-carbon black stock with sulfur and tertiary-bu- Table II tyl peroxide.

Four separate stocks of polyisobutylene were com- Mdu1uS(500% Elongation) pounded with the following ingredients in the proportions indicated. The mixing was done on a two-roll mill. Pam OWBHW; Peroxide Parts S lf Stock 5 1 2 4 6 8 Compounding Ingredients A B O D 2 115 175 190 3 200 225 200 180 4 250 260 265 275 Polyisobutylene 100 100 100 100 e 3 330 290 310 Oa l a gn Black 6(5) 50 5 y Peroxide 5 5 In the presence of at least one part of sulfur, additions of t-butyl peroxide in excess of one part per 100 parts of The four stocks were then heated in a press for polyisobutylene cause curing of the polyisobutylene. The minutes at 145 C. The pertinent physical properties of 50 amount of cure is proportional to the amount of t-butyl the resultant products are indicated in the following table: peroxide added on the mill, up to about 7 parts, while Table 1 larger amounts of the peroxide cause a blowing of the stock. Blowing sometimes takes place when smaller stock amounts of the peroxide are used. It generally can be Ph IP H 55 avoided by cooling the stock before removal from the ysma press in which it is cured. In general, from about 2 to A B 0 D about 7 parts of t-butyl peroxide per parts of polyisobutylene are preferred. gcegtcair'll zefisgg 1 328 1, S38 (Tar) $33 The time of heating necessary to achieve a satisfactory fi gg g gflgfig i sf g m 58 3 8 0 cure varies somewhat with the temperature of the cure. a e 0 E5 on) At higher temperatures, e. g., about 175 C., a good cure is obtained in about one hour, whereas at lower tempera- The matenany hlghe? tensle Strength and modulus of tures, e. g., C. it takes about six hours to obtain a stock D as compared Wlth stock A Show that q D has cure comparable to that obtained in one hour at 175 C. been cured. The fact that stock B has substantially the 65 A curing time of from one to two and one ha1f hours same physical properties as stock A shows that the use at a temperature between C. and C. is of sulfur alone Wlll not cause polyisobutylene to cure. ferred S1m1larly, the fact that stoclt C is completely deteriorated The curing action efiected by the sulfur and the t buty1 indicates that t-butyl peroxide alone will not cause the peroxide in the process f my invention takes Place in elastomel' to Cure- 70 polyisobutylene gum stocks and in polyisobutylene stocks The increase in the modulus and tensile strength, illustrated by stock D, is representative of the results obtained containing non-black fillers, e. g., zinc oxide, as well as in polyisobutylene stocks containing carbon black. The

cure in the gum stocks and non-black-reinforced stocks is evidenced by the insolubility of these stocks in cyclohexane after treatment by the process of my invention.

Having thus described my invention, What I claim and desire to protect by Letters Patent is:

A method of curing elastomeric polyisobutylene which comprises incorporating in the elastomer at least about one percent by weight of sulfur, and from about 2 to 7 4 percent by weight of tertiary-butyl peroxide, based on the Weight of the uncured polyisobutylene, and heating the mixture at a temperature of at least about 145 C. and for a time suflicient to cure the polyisobutylene.

UNITED STATES PATENTS References Cited in the file of this patent 2,582,510 Stiratelli h---"- Jan. 15, 1952 

